With production booming in the Bakken oil field along the U.S. northern tier and in Canada, some experts say stronger rules to head off a catastrophe are long overdue. However, drafting and approving new regulations can take months or even years, an elaborate process that involves time to study potential changes and a public comment period before anything is adopted.

In the latest crash, a CSX train carrying Bakken crude from North Dakota derailed Wednesday in downtown Lynchburg, sending three tanker cars into the James River and shooting flames and black smoke into the air. No one was injured, but the wreck prompted an evacuation and worried local residents and officials.

There have been eight other significant accidents in the U.S. and Canada in the past year involving trains hauling crude, and some of them caused considerable damage and deaths, according to the National Transportation Safety Board. Bakken crude ignites more easily than other types.

The NTSB and members of Congress have been urging the Transportation Department to work swiftly on new standards that would make tanker cars more rugged.

"Everybody is waiting on them and expecting some significant action," Grady Cothen, a former Federal Railroad Administration official, said after Wednesday's wreck. "It's a front-and-center concern on the part of everybody in rail transportation."

Transportation Secretary Anthony Foxx has told lawmakers that regulators are working as quickly as they can to get tougher tanker car regulations written and approved.

But he said some oil companies have failed to provide the data he requested, and he complained that the agency within his department that regulates flammable liquids is understaffed.

"We have a million shipments of hazardous materials moving around this country every day, and we have 50 inspectors," Foxx told The Associated Press recently.

The cause of the accident is under investigation by the NTSB. CSX said it is cooperating fully.

NTSB investigator Jim Southworth said the train was going 24 mph in a 25 mph zone at the time.

Tom Shahady, a professor of environmental science at Lynchburg College, said erosion around the tracks because of increased development may have contributed to the derailment.

On Thursday, crews used cranes and other heavy equipment to clear the wreck, and workers put a boom around the cars in the water. Nearly all the train's cars were carrying crude, and each had a capacity of 30,000 gallons, officials said.

"This could have been a whole lot worse," Mayor Michael A. Gillette said, adding that local officials have virtually no say over railroad operations. "We rely on state and federal government to do the work that needs to be done that our citizens are safe."

Lorrie Saunders looked at the wreck and said: "It was a miracle it didn't set the whole town of Lynchburg on fire."

On Thursday, the Virginia Department of Emergency Management estimated that 20,000 to 25,000 gallons of oil had escaped, said spokeswoman Dawn Eischen. It wasn't clear how much burned off and how much entered the river. The figure was much lower than an estimate given by city officials the previous day.

City spokeswoman JoAnn Martin said there was no effect on the water supply for Lynchburg's 77,000 residents because the city draws from the river only during droughts.

The spill probably won't have a significant effect on the James River, given its volume and the other pollutants that already flow into it, Shahady said. Department of Environmental Quality spokesman Bill Hayden said that there appears to be sheen on the water but that officials do not believe it poses a serious environmental threat.

Concern about rail safety grew last July when a runaway oil train derailed and exploded in Lac-Megantic, Quebec, near the Maine border. Forty-seven people died and 30 buildings were incinerated.

Canadian investigators said the 1.3 million gallons of Bakken crude released in the accident was comparable in combustibility to gasoline.

The NTSB has long recommended that the Transportation Department toughen its design standard for oil tanker cars, saying they are too easily punctured or ruptured, even in low-speed accidents.

"We are very clear that this issue needs to be acted on very quickly," NTSB chairwoman Deborah Hersman warned in one of her last acts before leaving office last week.

On Thursday, former NTSB chairman Jim Hall sent a letter asking the transportation secretary to impose a 20 mph speed limit on oil trains through all communities until new, more durable tanker cars are built and older ones retrofitted to make them more robust.

Earlier this year, the freight industry agreed to restrict oil trains to 40 mph. But Hall said: "These tank cars have a very high failure rate at speeds below the industry's new voluntary speed limit."